A known optical device such as an optical communication laser diode (LD) module includes a thermoelectric conversion module for controlling the temperature of the optical device such as a laser diode, a package (housing) for keeping its airtightness and a mount to which the optical device is mounted.
The thermoelectric conversion module disclosed in JP2004-301873A is fixed in the package, and the mount, to which the optical device is mounted, is fixed on an upper surface of the thermoelectric conversion module.
The mount is made of a copper-tungsten alloy (Cu/W alloy) or an iron-nickel-cobalt alloy (Fe/Ni/Co alloy).
As shown in FIG. 4, another known thermoelectric conversion module, which is disclosed in JP2004-014995A, includes two insulated substrates, each of which has same thickness, and plural thermoelectric element (a P-type thermoelectric element and a T-type thermoelectric element) are provided between the two insulated substrates so as to be aligned on the counter surfaces and sandwiched therebetween. Specifically, the thermoelectric elements are soldered to electrodes, which are formed on each counter surface of the insulated substrates. The insulated substrate is made of alumina.
Generally, when the laser diode is mounted on the mount as an optical device, the temperature of the laser diode is increased because of a laser emission. In order to reduce the temperature of the optical device, a direct-current electricity is applied to the thermoelectric conversion module in a manner where the insulated substrate to which the mount is jointed is set as a cooling-side, and the insulated substrate which is joined to a bottom portion of the package is set as a cooling-side.
Then, the insulated substrate on the cooling-side and the mount shrink due to the reduction of their temperatures, and the insulated substrate on the heat dissipating-side and package expand due to the increment of their temperature. Because of such shrinking or expanding, stress is applied to the thermoelectric elements, which are provided between both insulated substrates so as to be soldered to each of the insulated substrates.
The level of stress varies depending on a material of the member that is joined to each of the insulated substrates such as the mount and the bottom portion of the package. Specifically, when the mount is made of Fe/Ni/Co alloy and the bottom proportion (bottom plate) is made of Cu20/W80 alloy, larger stress is applied to the thermoelectric conversion. In other words, the larger the difference between the linear expansion coefficient of the mount and the liner expansion coefficient of the bottom portion of the base portion of the package become, the more the thermoelectric conversion module is stressed. Thus, a crack or a separation occur on the joint portions between the thermoelectric element and each of the mount and the base portion of the package, as a result, a level of the cooling ability has been reduced.
A need thus exists to provide a thermoelectric conversion module and an electronic device to which the thermoelectric conversion module is mounted which reduce the level of stress applied to the thermoelectric element.